1. Field of the Invention
The invention relates to xe2x80x9cone-wayxe2x80x9d clutches wherein a plurality of struts provide a mechanical couple between the opposed clutch faces of a pair of coaxial rotatable members.
2. Background Information
Clutches are used in a wide variety of applications to selectively couple power from a first rotatable xe2x80x9cdrivingxe2x80x9d member, such as a driving disk or plate, to a second, independently-rotatable xe2x80x9cdrivenxe2x80x9d member, such as a driven plate or disk. In one known variety of clutches, commonly referred to as xe2x80x9cone-wayxe2x80x9d or xe2x80x9coverrunningxe2x80x9d clutches, the clutch xe2x80x9cengagesxe2x80x9d to mechanically couple the driving member to the driven member only when the driving member seeks to rotate in a first direction relative to the driven member. Once so engaged, the clutch will release or decouple the driven member from the driving member only when the driving member rotates in a second, opposite direction relative to the driven member. Further, the clutch otherwise permits the driving member to freely rotate in the second direction relative to the driven member. Such xe2x80x9cfree-wheelingxe2x80x9d of the driving member in the second direction relative to the driven member is also known as the xe2x80x9coverrunningxe2x80x9d condition.
One such known one-way clutch employs juxtaposed, nominally-coaxial driving and driven members featuring generally planar clutch faces in closely-spaced axial opposition. Such xe2x80x9cplanarxe2x80x9d one-way clutches, as taught by Frank in U.S. Pat. No. 5,449,057 and Ruth et al. in U.S. Pat. No. 5,597,057, typically include a plurality of recesses formed in the face of the driving member and at least as many recesses formed in the face of the driven member. A thin, flat strut is carried within each of the driving member""s pockets such that a first longitudinal end of each strut may readily engage and bear against a shoulder defined by its respective recess of the driving member. The strut""s second, opposite longitudinal end is urged toward and against the face of the driven member, for example, by a spring positioned beneath the strut in the recess of the driving member.
When the driving member rotates in the first direction relative to the driven member, the second end of at least one strut engages and thereafter bears against a shoulder defined by a recess of the driven member, whereupon the strut is placed in compression and the driven member is coupled for rotation with the driving member. When the driving member rotates in the second direction relative to the driven member, ramped surfaces defined by other portions of the driven member""s recesses urge the second end of each strut back towards the driving member, whereupon the driving member is permitted to freely rotate in the second direction relative to the driven member.
This periodic engagement of the second end of each strut with the ramped surfaces of the driven member""s clutch face during clutch overrun may generate a noise or xe2x80x9cratchetingxe2x80x9d sound that is often associated with one-way clutches. Known approaches to reduce this ratcheting sound during clutch overrun include modifications to the design of the strut, including reductions in the strut""s inertial mass; modifying the spring forces exerted on the strut; and the use of various motion-damping fluid in the space between the clutch faces to thereby better control the dynamics of the strut during clutch overrun. However, further improvement in noise reduction during overrun is desirable, particularly as other clutch components, such as the driven member, become fabricated from materials exhibiting different noise-transmissive characteristics, for example, powdered metal.
It is an object of the invention to provide a one-way clutch assembly which features improved noise characteristics
Under the invention, a one-way clutch assembly includes a first member rotatable about a first axis, wherein the first member includes a coupling face having a recess defining a load-bearing shoulder; and a second member, also rotatable about the first axis, wherein the second member includes a coupling face, positioned in close-spaced opposition with the coupling face of the driving member, that defines a reference surface which, in an exemplary embodiment, is generally normal to the first axis. The coupling face of the driven member includes a plurality of recesses, with each recess defining a load-bearing shoulder and a ramped surface opposite to the shoulder. The ramped surface includes a convex surface portion that tangentially intersects the reference surface and, preferably, also tangentially intersects a further generally flat surface portion of the ramped surface within the recess of the driving member. A base surface of the recess is also preferably disposed between the flat surface portion and the shoulder of the recess.
The clutch assembly in accordance with the invention also includes a strut disposed between the coupling faces of the members. Each strut is moveable between a first position characterized by simultaneous abutting engagement of a respective end of the strut with a respective shoulder of each member, and a second position characterized by non-engagement of the strut with at least the second member. Significantly, under the invention, the convex surface portions of the ramped surfaces periodically engage the strut upon rotation of the second member in a first direction relative to the first member to urge the strut toward the second position. In this manner, each strut is xe2x80x9ccammedxe2x80x9d by the convex surface portions to the second position, resulting in a reduction in generated noise during overrun while achieving improved strut stability.
While the invention contemplates any suitable geometry for the convex surface portion of the ramped surfaces, in accordance with a feature of the invention, the convex surface is preferably defined by a curved portion of the ramped surface and, most preferably, the curved portion has a substantially constant radius of curvature. Thus, in a preferred embodiment, wherein each strut includes a pair of diametrical member-engaging ends separated by a nominal longitudinal dimension d, the substantially constant radius of curvature is greater than about d/10.
While an exemplary clutch assembly in accordance with the invention is illustrated and disclosed, such disclosure should not be construed to limit the claims. It is anticipated that various modifications and alternative designs may be made without departing from the scope of the invention.